The present invention relates to nebulizers for inhalation therapy. It more particularly concerns a nebulizer having improved large water droplet removal capability and an improved heating arrangement.
In common forms of inhalation therapy, oxygen or an oxygen enriched mixture of air is provided for introduction to a patient's lungs by means of suitable breathing apparatus. The gas mixture is preferably moisturized and transmitted to the patient through a flexible tube which may be several feet or more in length. Particularly where such a tube is corrugated, but even where it is not, water in the moisturized gas mixture tends to drop out of the mixture, collecting in lower portions or bends of the connecting conduit. The water collected in the conduit may increase in volume to a point where the connecting conduit is either partially or entirely blocked, thereby greatly endangering the patient by obstruction of the supply of breathable gas.
The nebulizer provides a gas stream that entrains water particles rather than water vapor (as in a humidifier). It requires a minimum water particle size because it must insure that water particles will reach deeper portions of the respiratory tract. In a humidifier the gas carries water vapor rather than water particles and the moisture in the inhaled mixture may be absorbed before it reaches deeper portions of the respiratory tract. In the nebulizer, liquid particle size preferably is from about five microns down to about two microns. Particles larger than five microns have a greatly increased tendency to drop out of the mixture during flow from the nebulizer to the patient. It is these large size particles that must be avoided. Thus, large particles in the mixture do no good to the patient because they generally do not remain in the mixture for time long enough to reach the patient. But more importantly, they tend to collect and fully or partially occlude the connecting tubing, requiring frequent attention and draining of the tubing to avoid complete blocking of flow.
Prior attempts to remove larger droplets from the inhalation mixture are basically ineffective, inefficient, complex, and costly. For example, the patent to Cronenberg, U.S. Pat. No. 4,243,396, describes a tortuous spiral path formed between a pair of telescoping tubes as a separator of gas droplets. The patent to Kienholz et al., U.S. Pat. No. 4,267,974, describes a chamber which is termed a baffling chamber having a baffle plate at the chamber exit. The patent to Schwartz al., U.S. Pat. No. 4,177,945, shows a tortuous path that results in turbulent flow for removal of liquid droplets. These arrangements are largely ineffective, greatly complicating nebulizer structure, thereby increasing costs and compromising efficiency.
A nebulizer is employed to provide a gas mixture that will vary from 100% oxygen (less water content) to as little as 28% oxygen. Thus, the nebulizer is provided with an adjustable air intake through which selectively varying amounts of air are admitted to the mixing chamber for mixing with the oxygen that is supplied under pressure. Such air quantity adjusting devices frequently take the form of a sleeve rotatable about an apertured tube with the tube apertures being completely overlapped by the sleeve in the desired 100% oxygen condition. However, the rotatable aperture closing sleeve must be made with tolerances that always result in some space between the sleeve and the tube. This allows some air to be drawn into the mixing chamber even when the adjusting sleeve is in the closed position. Thus with prior nebulizers having an adjustable air intake, it is not possible to achieve the desired 100% oxygen condition.
When the nebulizer involves a heater for controlling temperature of the moisturized breathing mixture, the problem of large droplet fallout is increased, yet the prior art does not recognize or attempt to solve this problem. In the heated mixture, the larger particles are more of a problem because small droplets tend to condense upon the big ones thereby significantly increasing the problem of droplet fallout. Neublizer heaters of the prior art fail to suggest a solution for, or even to recognize, such problem.
Accordingly, it is an object of the present invention to provide a nebulizer that avoids or minimizes the above mentioned disadvantages.